Using X-Parameters* to Generate IBIS Models

Transcription

1 Using X-Parameters* to Generate IBIS Models Tom Comberiate and José Schutt-Ainé University of Illinois at Urbana-Champaign European IBIS Summit May 15, 2013 Paris, France *X-Parameters is a registered trademark of Agilent Technologies.

2 Outline Motivation Background IBIS Model Construction X-parameter File Generation Simulations to Produce IBIS Model Conclusions/Comments Future Work 2

3 Motivation IBIS models can be difficult to generate, especially without revealing IP to the model generator. NC State s s2ibis3 [1] is still the open-source standard for simulated IBIS generation [2]. X-parameters [3]: Are behavioral, protect IP. Are the large-signal extension of S parameters. Can describe nonlinear effects. Can be measured with an NVNA [4]. Would like for designers to be able to exchange.xnp files and generate IBIS models from them. 3

4 Polyharmonic Distortion (PHD) Model [5] Linearization of a nonlinear function around a largesignal tone A 1,1 applied at the input. Multiple harmonic inputs with dominant fundamental Fundamental behaves nonlinearly Harmonics follow superposition and contribute to the others. Nonlinear 2-Port Device A 1,1 A 1,2 A 1,3 A 2,1 A 2,2 A 2,3 B 1,1 B 1,2 B 1,3 B 2,1 B 2,2 B 2,3 4

5 X-Parameters Formalism [5] Approximates Incident Waves frequency Bpk, ( DC, A1,1, A2,1, A1,2, A2,2, A1,3, A2,3, ) Nonlinear Mapping X ( DC, A,0,0, ) ( FB) pk, 1,1 Simple Nonlinear Mapping frequency ( S) ( T) * X p, k; q, l ( DC, A1,1 ) Aq, l X p, k; q, l ( DC, A1,1 ) A q, l frequency A 1,1 Large- Signal Nonanalytic Harmonic Superposition Scattered Waves frequency frequency frequency 5

6 X-Parameters Formalism [5] q N, l K q N, l K ( FB) k ( S ) k l ( T ) * p, k p, k p, k; q, l q, l p, k; q, l q, l k l q 1, l 1 q 1, l 1 ( q, l) (1,1) ( q, l) (1,1) B X P X A P X A P Simple nonlinear map Linear harmonic map function of incident wave Linear harmonic map function of conjugate of incident wave B p,k and A q,l are harmonic wave components. FB-, S-, and T-parameters are functions of frequency large-signal magnitude A 1,1 DC bias output port X ( S ) p, k ; q, l output harmonic input port P input harmonic 6 A A 1,1 1,1

7 IBIS Model Construction Starting point: SPICE netlist for basic inverter, V cc = 2.5 V. Goal: IBIS file of output model Include I-V and V-t curves. Exclude parasitics, clamps, and AMI [6]. 7

8 Rules/Guidelines Only generating X-parameter data that could be measured with a real NVNA. Using the IBIS Cookbook v4.0 as a guide to generate I-V and V-t curves [7]. Comparing results to those generated with s2ibis3. 8

9 x2ibis Flowchart 9

10 Generating X-Parameters X-parameters generated with Harmonic Balance simulation. Need to set proper values for: Frequency range Fundamental power DC bias X-parameter measurements are unidirectional because of large-signal fundamental A 1,1 on one port. Different types of X-parameter ports [8]: Source Load Bias 10

11 x2ibis Flowchart 11

12 I-V Curve Generation Test Circuit Voltage Stimulus +2V cc In Out Z c k A 1,1 DC Bias = +0.5V cc DC Voltage Bias X-Parameter Source Current Response -V cc Approximate DC with low frequency voltage sweep and measure current response. 12

13 x2ibis Flowchart 13

14 V-t Curve X-Parameter Generation k A 1,1 DC Bias = +0.5Vcc Inverting Buffer X-Parameter Stimulus Falling Rising Response Rising Falling +Vcc Gnd Z c In X-parameter Source Test Circuit Out X-parameter Load Z c Approximate step functions with rising and falling portions of a sinusoid. 14

15 What We Have 2.xnp files I-V.xnp file 1 2 Out In/Bias V-t.xnp file 1 2 In Out 1-port measurement 1 fundamental frequency (low) 11 harmonics 1 power level, 2 input bias levels 26 kb 2-port measurement 1 fundamental frequency (high) 7 harmonics 1 power level, 2 input bias levels 39 kb 15

16 Simulating with X-Parameters Can only use X-parameter data in Harmonic Balance (HB) simulations, which are steady-state (periodic). Use scattered and incident waves to calculate voltage and current needed for IBIS tables. V A B Ia a a a 1 ( ) 0 Aa Ba 16 Z

17 x2ibis Flowchart 17

18 I-V Curve Calculation from X- Parameter Measurement Z c I-V.xnp file 1 2 Out In/Bias Harmonic Balance Source DC Voltage Bias Apply 1-tone voltage stimulus same as for generation. Measure input current and plot against input voltage. Normalize voltage so curve goes through (0 V, 0 ma). 18

19 Current (A) Current (A) I-V Curve Generation Results 30.0m 20.0m 10.0m m -20.0m Pullup Curve x2ibis s2ibis Voltage (V) 50.00m 25.00m 0.00 x2ibis s2ibis Pulldown Curve m Voltage (V) x2ibis and s2ibis have excellent match 19

20 x2ibis Flowchart 20

21 V-t Curve Calculation from X- Parameter Measurement Harmonic Balance Stimulus k A 1,1 DC Bias = +0.5Vcc Inverting Buffer Falling Rising Response Rising Falling +Vcc Gnd Z c V-t.xnp file 1 2 In Out Harmonic Balance Source 50 Ω Approximate a step function with a sinusoid. Generate V-t rising and falling curves from the corresponding portions of the response to the stimulus. Normalize beginning and end points to match I-V data. 21

22 Voltage (V) Voltage (V) Voltage (V) Voltage (V) V-t Curve Generation Results Falling Vcc Rising Vcc s2ibis x2ibis s2ibis x2ibis n 2.0n 3.0n n 2.0n 3.0n time (seconds) time (seconds) Falling Gnd Rising Gnd s2ibis x2ibis 0.2 s2ibis x2ibis n 2.0n 3.0n time (seconds) n 2.0n 3.0n time (seconds) x2ibis and s2ibis have reasonable match 22

23 voltage (V) Putting It All Together Comparison of x2ibis and s2ibis models with PRBS stimulus: x2ibis s2ibis 0.0 x2ibis and s2ibis match well n 400.0n 600.0n 800.0n 1.0µ time (seconds) 23

24 Conclusions/Comments Only 2 small X-parameter files needed, <100kB. IBIS data is generated in a seamless manner. Ability to include second-order effects to improve accuracy. Could include multiple frequencies in the V-t curve.xnp file to vary rise times. Ideally, these.xnp files could be sent to model developer instead of SPICE netlist. 24

25 Future Work Improve approximation of ideal step for V-t curve generation. Perform x2ibis on more complicated buffer circuits. Include parasitics, clamps, etc. Include equalizer blocks Develop transient simulation techniques for use with.xnp files. Implement BIRD releases (95 & 98) 25

26 Acknowledgments Signal Integrity Research Group at the University of Illinois at Urbana-Champaign. Xu Chen Agilent Technologies, Inc. for providing the X-parameter platform. Loren Betts Steve Fulwider David Root Eric Iverson This research was made possible with United States Government support under and awarded by DoD, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168a and through the support of the National Science Foundation. 26

27 References [1] s2ibis3 v1.1. Copyright North Carolina State University. Last modified: March 27, [2] C. Warwick, What About the *.ibs File? blog, 15 December, 2011; [3] X-Parameters Trademark Usage, Open Documentation and Partnerships, d=zzfindeesof-x-parameters-info. [4] Agilent Technologies, PNA-X Nonlinear Vector Network Analyzer (NVNA), January and-520. [5] L. Betts, Agilent Technologies, X-Parameters & Nonlinear Vector Network Analysis (NVNA) Going Beyond S Parameters, May 9, [Online]. Available: [6] The IBIS Open Forum, I/O Buffer Information Specification Version 5.1. Ratified August 24, IBIS homepage: [7] The IBIS Open Forum, IBIS Modeling Cookbook for IBIS Version 4.0, Copyright 2005 Government Electronics and Information Technology Association and The IBIS Open Forum. [8] Agilent Advanced Design System, Version Help Notes, X-Parameter Generator Basics ADS help notes on X-parameter ports. Copyright , Agilent Technologies. 27